Onshape Learning Center with the beginner pathways, plus an “Intro to CAD” curriculum that’s classroom-ready.
Good options for middle school beginners:
Learning Center (self-paced): start with the CAD Basics pathway, then Onshape Fundamentals: learn.onshape.com
Intro to CAD curriculum: designed as a semester-ish sequence, with teacher guides + student guides + slides and starter documents: Learning Center overview + curriculum info
Educator hub: curated resources for teaching, including “Teaching a Class in Onshape”: Educator resources